Yaesu FT-301D Manuel utilisateur

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Modification VFO

reversal of rotations

Yaesu FT-301D

Modification instructions

April 10, 2019

Mod-VFO Drehrichtung_en.docx January 28, 2019, © Elcon, Switzerland Seite 2 / 7

Table of Comments

1Introduction ..................................................................................................................................... 3

2Changing the direction of rotation of the variable capacitor ........................................................... 4

2.1 Removing the spreaders in the VFO variable capacitor ........................................................ 4

2.2 Mechanical adjustment of the VFO variable capacitor........................................................... 5

2.3 Functional test........................................................................................................................ 6

3Changing the direction of rotation on the CALIB knob ................................................................... 6

4Disclaimer of liability ....................................................................................................................... 7

Important! Advices or tips for the correct function.

Caution! The instructions must be observed carefully.

Mod-VFO Drehrichtung_en.docx January 28, 2019, © Elcon, Switzerland Seite 3 / 7

1 Introduction

Normally you are used to turning the VFO knob clockwise increasing the frequency and vice

versa. With the FT-301D it is just the other way around and therefore very unusual.

This is due to the frequency conditioning of the FT-301.

Figure 1

As shown in Figure 1, the VFO frequency is subtracted from the crystal frequencies for the

different bands (Band Crystal). Thus, the VFO frequency runs in opposite direction to the

premixer frequency and thus also to the transmit frequency (Tx frequency).

Figure 2

The variable capacitor of the VFO is designed in such a way that the rotor plates turn out

clockwise and thus the capacity decreases -> the frequency of the VFO increases -> the Tx

frequency decreases.

As shown in Figure 2, the fiber glass spreaders on the two rotor plate packs prevent them

from being turned counterclockwise beyond the maximum capacity. However, this would be

absolutely necessary to reverse the frequency to the direction of rotation.

Spreader

Mod-VFO Drehrichtung_en.docx January 28, 2019, © Elcon, Switzerland Seite 4 / 7

The American amateur radio friend David, N0EDS, had the great idea to remove the two

spreaders so that the variable capacitor could be rotated freely through 360°.

The following description shows how the modification is carried out.

2 Changing the direction of rotation of the variable capacitor

2.1 Removing the spreaders in the VFO variable capacitor

Remove the four screws and the VFO cover.

Remove very carefully, without bending the rotor plate of the variable capacitor VC801,

both fiber glass spreaders with a small side cutter.

Figure 3

Place the device upright in front of you so that you can work well on the rotor plates.

Cover the lower part of the variable capacitor with a cloth to prevent filings from entering

the unit. (see Figure 4).

Figure 4

Carefully deburr all ends of the rotor plates with a needle file on the side where you have

removed the spreaders.

Mod-VFO Drehrichtung_en.docx January 28, 2019, © Elcon, Switzerland Seite 5 / 7

Under no circumstances should the rotor and stator plates touch each other!

Remove the cloth carefully so that no metal chips fall into the device.

Clean the capacitor between the plates with a contact spray so that there are no more

aluminum filings inside.

2.2 Mechanical adjustment of the VFO variable capacitor

Turn the unit, so that the open variable capacitor is easily accessible from above and the

tuning knob at the front.

Loosen (do not unscrew!) the two grub screws of the gear wheel on the axis of the rotary

capacitor. The tuning knob must be turned slightly, as both screws are not accessible at

the same time).

Figure 5

Position the variable capacitor by hand so that the rotor plates are fully turned in

(maximum capacity of the variable capacitor), see Figure 6).

Figure 6

Turn the tuning knob clockwise to the right stop. The variable capacitor must not rotate,

otherwise you have not loosened the grub screws enough.

Mod-VFO Drehrichtung_en.docx January 28, 2019, © Elcon, Switzerland Seite 6 / 7

In this position tighten the grub screw accessible from above.

Turn the tuning knob counterclockwise until you see the second grub screw and can

tighten this one too.

2.3 Functional test

Turn on your transceiver. Set the receiver in the 20m band, USB with "Tune" to maximum

noise in the speaker.

Check by slowly turning the VFO knob whether you can hear the noise over the entire

tuning range without interruption.

If the noise suddenly decreases at any position of the VFO knob, the rotor plates of the

variable capacitor are touching the stator. In this case, check the capacitor carefully with a

magnifying glass.

3 Changing the direction of rotation on the CALIB knob

Turn the unit upside down so that the underside faces upwards.

Solder off the two resistors R14 (1kΩ) and R15 (3.3kΩ) from the CALIB potentiometer

VR6 (5kΩ), see Figure 7 .

Figure 7

Solder the two resistors R14 (1kΩ) and R15 (3.3kΩ) in the swapped positions to the

CALIB potentiometer VR6 (5kΩ), see Figure 8

Figure 8

Mod-VFO Drehrichtung_en.docx January 28, 2019, © Elcon, Switzerland Seite 7 / 7

4 Disclaimer of liability

Any actions based on the information contained in this document are taken at the user's own

responsibility. Any liability is excluded, both for direct and indirect damages and

consequential damages that may arise in connection with the use of the information

contained in this document.

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